LYMPHOCYTES & ITS FUNCTIONS BY MADAM NELOFAR SULTANA DEPTT. OF PHYSIOLOGY DMC, KARACHI

LEARNING OBJECTIVES TYPES OF LYMPHOCYTES By the end of lecture the student Should be able to TELL: TYPES OF LYMPHOCYTES SPECIFICITY OF ANTIBODIES & SENSITIZED T- CELLS. CLONES OF LYMPHOCYTES. ACTIVATION OF T LYMPHOCYTES BY HELPER T- CELLS

LEARNING OBJECTIVES FORMATION OF ANTIBODIES. DIFFERENCE B/T PRIMARY & SECONDARY RESPONSE. NATURE OF ANTIBODIES. CLASSES OF ANTIBODIES. MECHANISM OF ACTION OF ANTIBODIES. TYPES & FORMATION OF T-CELLS.

Lymphocytes T cells or T Lymphocytes B cells or B Lymphocytes NK Cells mature in thymus gland Cell mediated immunity B cells or B Lymphocytes mature in bone marrow antibody-mediated immunity NK Cells

Figure 22.5 The Derivation and Distribution of Lymphocytes Figure 22.5a-c

T-LYMPHOCYTES Immature lymphocytes leave bone marrow during fetal and early neonatal life. Go to thymus gland. Mature there before they go on to other lymphoid tissues. These are T-lymphocytes. Also, and lymphocyte that is derived from one of these original T-lymphocytes via mitosis is also a T-lymphocyte.

T-LYMPHOCYTES Do not produce antibodies. Function in “cell-mediated immunity.” “NATURAL KILLER” cells destroy viruses. Secrete “lymphokines” which attract phagocytic cells. Secrete “perforin” which eats holes in the cells membrane or viral coat of invaders. “Helper T cells”: Induce macrophages to destroy other antigens STIMULATE B-LYMPHOCYTES TO PRODUCE ANTIBODIES. (Can help hundreds of B-lymphocytes mature by releasing “B-cell growth factor.”) “Suppressor T Cells” prevent overreaction of the system. (Inhibit B-lymphocye production.)

B-LYMPHOCYTES Mature in bone marrow, then carried to lymphoid tissue via blood stream and lymphatic circulation. This process of maturation and migration takes place throughout life. Other lymphocytes can be generated via mitosis of B lymphocytes resident in lymphoid tissues.

B-lymphocytes - function B-cells activation: 1/ thymus independent – polysacharide antigens, a cooperation with T cells is not necessary for B cells activation 2/ thymus dependent - first of all, the development of antigen-specific Th cells is necessary, then, thanks to cooperation between B cells and Th cells the antibody production could be sufficient and appropriate

B-lymphocytes - function Antibody production Antigen presentation

Activation of Lymphocytes in Lymph Nodes

ANTIGENS A foreign substance or organism. Any substance against which an antibody is produced. They have a molecular weight of 8,ooo and above More specifically, antigens are proteins or polysaccharides on the cell surface of an invading organism.

Innate and adaptive immune responses:

SPECIFIC IMMUNITY The body must be able to recognize the difference between “self” and “nonself.” (Any lymphocytes with antibodies that recognize one’s own body tissue as an antigen ar ekilled during fetal life.)

STAGES OF SPECIFIC IMMUNE RESPONSE (1) Antigen encounter and recognition by lymphocytes. (2) Lymphocyte activation. (3) Attack.

(1) Antigen encounter and recognition by lymphocytes Specific lymphocytes are programmed to recognize a specific antigen. This usually happens in a lymphoid organ, bloodstream, or lymph vessel. (This could take quite some time…)

(2) LYMPHOCYTE ACTIVATION Once a lymphocyte has recognized an antigen, it undergoes numerous cycles of mitotic divisions, making more of the same. Some of the newly produced cells carry out the attack; others influence the activation and function of the attack cells.

(3) ATTACK B-lymphocytes have specific receptors on their cell membrane – ANTIBODIES – that bind with invading materials/organisms.

ANTIBODIES Proteins produced by lymphocytes in response to an antigen. They bind to specific sites on antigen surfaces. Antibodies don’t kill organisms. However, they: can inactivate an invader, and initiate the process of activating phagocytic cells and other natural killers. Can combine with bacterial toxins or viruses to prevent attachment to target cells (“inactivation”). There is a SPECIFIC antibody for any one given type of individual invader.

ANTIBODY STRUCTURE (Remember, they belong to group of plasma proteins called “globulins.”) Made up of four polypeptides (amino acid chains). Two heavy chains, two lighter chains. Have the shape of a letter “Y”. Intersection of arms and base of “Y shape” is flexible, allowing deformation of antibody when it attaches to an antigen.

VARIABLE REGION OF ANTIBODIES At the tip of the arms of the Y-shape. Variable region has the potential to bind with particular classes of antigens. Once a raw antibody is stimulated to fit to a specific antigen, it can then react with ONLY that antigen. This is known as SINGLE SPECIFICITY. Can fit as precisely as a lock-and-key to an antigen.

TYPES OF ANTIBODIES Because they are involved in immune response, they are called immunoglobulins, abbreviated Ig…

SUMMARY OF IMMUNOGLOBULINS

Ontogenesis of the antibody production Although the production of specific antibodies already begins about week 20-24 of gestation, IgA+M concentrations are very low until the birth IgG production begins only after the birth, but IgG level is at this time sufficient thanks to maternal IgG About 4 to 6 months of age maternal IgG is eliminated from the child’s organism (possible onset of humoral deficiency symptoms)

PRIMARY IMMUNE RESPONSE B-lymphocyte – antigen contact induces mitosis (plasma cells) for more antibody carrying cells. Antibodies released to circulatory systems. SECONDARY IMMUNE RESPONSE Some “activated B-lymphocytes” become plasma cells. Some remain smaller, but retain antigen-recognition ability. (B memory cells) Next time similar antigen is encountered, response is MUCH FASTER due to resident and waiting memory cells.

Primary vs. Secondary Ab responses

Overview of the Immune Response

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